The evolution from wireless based voice only communication networks to wireless based voice and data communication networks has resulted in the development of general packet radio service (GPRS) and enhanced data rates for the global system for mobile communications (GSM) standards. Although speech still remains the dominant service by many cellular service providers, existing systems are being upgraded to provide greater support for data communication via the radio interface.
In digital communications, modulation signals may be expressed in terms of I and Q components, which may be a rectangular representation of a polar diagram. FIG. 1 is a diagram illustrating the inphase and quadrature (I-Q) format utilized in digital communications. On a polar diagram, the inphase (I) axis lies on the zero degree phase reference, and the quadrature (Q) axis is rotated by 90 degrees with respect to the inphase (I) axis. The signal vector's projection onto the I-axis is its I component and the projection onto the Q axis is its Q component.
With reference to FIG. 1, a circuit may have perfect I-Q matching when the I and Q components of a signal are exactly 90 degrees phase shifted. When the I and Q components of the signal are not 90 degrees phase shifted, the performance of the system may deteriorate. For example, in certain circuits where the I processing path and Q processing path are not equally loaded, the loading mismatch may cause degradation in system performance. In case of a divide-by-two circuit, I-Q mismatch may occur when the first divide-by-two circuit is not loaded symmetrically.
FIG. 2a is a block diagram illustrating asymmetric loading in a divide-by-two circuit. Referring to FIG. 2a, there is shown a system 200 that comprises a plurality of divide-by-two circuits 202 and 204. The divide-by-two circuit 202 may generate the I and Q components of a signal. The divide-by-two circuit 204 may be adapted to receive the I component and generate the I and Q components of a second signal, for example. The Q component generated by the divide-by-two circuit 202 may not be coupled to another divide-by-two circuit, which may cause asymmetric loading of the divide-by-two circuit 202. The asymmetric loading of the divide-by-two circuit 202 may cause I-Q mismatch resulting in a deteriorated performance. The divide-by-two circuit 202 may be adapted to generate an output quadrature Q signal, for example, for PCS/DCS band and/or 802.11 a/g operation. The divide-by-two circuit 204 may be adapted to generate an output quadrature Q signal, for example, for GSM 850/GSM 900 band and/or 802.11 a/g operation.
FIG. 2b is a block diagram that may be utilized to overcome the asymmetric loading problem associated with FIG. 2a. Referring to FIG. 2b, there is shown a system 220 that comprises a plurality of divide-by-two circuits 222, 224 and 226. The divide-by-two circuit 222 may generate the I and Q components of a signal. The divide-by-two circuit 224 may be adapted to receive the I component and generate the I and Q components of a second signal, for example. The divide-by-two circuit 226 may be adapted to receive the Q component and generate the I and Q components of a third signal, for example. This is an easy way to balance the I and Q paths. However, the divide-by-two circuit 224 may take up additional area. Furthermore, it may consume additional power, which is a premium in mobile devices such as cell phones.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.